540 BACTERIOLOGY. 
shorter and longer forms may also be seen, even grow- 
ing out into flexible filaments, which are sometimes 
more or less wavy or twisted like braids of hair. The 
bacillus does not form spores, and stains readily with 
fuchsin or gentian-violet. 
Biological Characters. An aérobic, facultative anaér- 
obic, liquefying, motile bacillus. Grows rapidly in 
the usual culture media at the room-temperature. 
Growth on Gelatin. The growth upon gelatin plates 
containing 5 per cent. of gelatin is very characteristic. 
At the end of ten or twelve hours at room-tem- 
perature small round depressions in the gelatin are 
observed, which contain liquefied gelatin and a whitish 
mass consisting of bacilli in the centre. Under a low- 
power lens these depressions are seen to be surrounded 
by a radiating zone composed of two or more layers, 
outside of which is a zone of a single layer, from which 
amceba-like processes extend upon the surface of the 
gelatin. These processes are constantly undergoing 
changes in their form and position. The young colo- 
nies deep down in the gelatin are somewhat more 
compact, and rounded or humpbacked; later they 
are covered with soft down; then they form irregular, 
radiating masses and simulate the superficial colonies. 
But it is difficult to describe all the forms which the 
proteus vulgaris takes on in all the stages of its growth 
on gelatin plates. When the consistency of the medium 
is more solid, as in 10 per cent. gelatin, the liquefac- 
tion and migration of surface colonies are more or less 
retarded. In gelatin stick cultures the growth is less 
characteristic—liquefaction takes place rapidly along 
the line of puncture, and soon the entire contents of 
the tube are liquefied. 
